1. Field of the Invention
The present invention relates to a golf ball manufacturing method. More particularly, the present invention relates to a method of removing a spew of a seam and making the seam smooth after the removal.
2. Description of the Related Art
A golf ball is usually formed by upper and lower molds having hemispherical cavities. A molding method such as an injection molding method, a compression molding method or the like is employed. By any molding method, a molding material slightly leaks out of a parting line of the upper and lower molds. Accordingly, a ring-shaped spew is generated in a portion corresponding to the parting line on the surface of the formed golf ball (which will be hereinafter referred to as a “seam”). In the injection molding method, agate is provided on the parting line of a mold. The spew is also generated in a portion corresponding to the gate. These spews are to be removed. The spew can be removed by methods disclosed in Japanese Laid-Open Patent Publications Nos. Sho 60-232861, Sho 63-174801, Sho 63-11266 and Hei 8-299498. In these spew removing methods, a spew is caused to abut on a cutting tool while a held golf ball is rotated. In these methods, the seam of the golf ball is rotated, and at the same time, the cutting tool is caused to abut in parallel with the direction of the rotation of the seam, thereby removing a spew. For the cutting tool, a grindstone, a sandpaper, a cutting tool piece or the like is used.
In the case in which the golf ball is to be formed by a compression mold, the flow of a resin in the seam is usually parallel with the seam. In some cases in which cutting or grinding is carried out in such a direction that the resin of the seam flows, the resin of the seam is removed unexpectedly when the seam abuts on a grinding tool or the like. In such seam removal, there has been found a phenomenon in which the material of the seam is often ground excessively to be scooped out when the grinding is particularly carried out by a rotation. Depending on the blending of the outer cover material of a ball, a molding method or the like, the orientation of the material in a seam portion is varied. In most cases, the flow of the material is parallel with or orthogonal to the seam.
Desirably, the seam of the golf ball is processed in such a manner as not to make a difference from a portion other than the seam of the golf ball after a spew is removed. In the case in which the direction of the processing of the spew is parallel with the spew, there is a phenomenon in which a cutting tool is apt to excessively cut or grind a material constituting the seam or the vicinity of the seam (hereinafter referred to as a “seam portion”). In this case, when the seam portion is processed at a time, the processing width of the seam portion tends to be increased. Such a processing damages the curved surface of the seam portion, which is not preferable. In respect of the aerodynamic characteristic of the golf ball, the uniformity of the surface of the golf ball is important. Also in some cases in which the seam portion has an unremarkable appearance which does not make a difference from other portions, a grinding mark remains microscopically. In the present invention, the grinding includes polishing.
In consideration of such problems, it is an object of the present invention to provide a golf ball having a higher uniformity by processing the seam of the golf ball more smoothly.